1. Field of the Invention
This invention relates to integrated circuit assemblies more particularly to an interconnecting assembly between integrated circuit package leads on a lead frame and the integrated circuit die.
2. Material Art
Interconnects between a semiconductive integrated circuit die and a metal lead frame have heretofore been made affixing a bonding wire between selected contact pads on the die and selected fingers of the lead frame. While originally this was a hand-operation, automatic wire bonding apparatus is conventionally used. There have been limitations in utilizing wire bonding when a high lead count of leads are required for connection with a centrally-mounted, increasingly smaller die with an increasingly larger number of die contact pads. To accommodate the centrally-mounted die and large number of die contacts the lead frame leads must be constricted in a converging pattern and even narrowed as they extend from the external portion of the leads to inner positions opposite the die contact pads. With an increasing number of leads in the lead frame and given a requirement for a minimum width of lead and a minimum spacing between the edges of adjacent leads, and the converging of the leads as they extend toward the die, the result is longer and longer wires extending from the lead frame leads to the die contact pads. For example, with 8 mil wide leads and 7-8 mil spacing between leads in a 68 or 84 leads lead frame the bond wire length between a convergent end of a lead to a die contact pad approaches about 150 mils. Such a length of the thin (outside diameter of 1.25 mil) gold wire can result in excess wire sag causing shorts between wires or result in wire "sweep" in which the thin long wire is swept away i.e. broken, during the subsequent package molding operations by flowing plastic encapsulant. In general, it has been found that the length of bonding wires should not exceed about 100 mils.
Improvements have been made by utilizing a so-called TAB (tape automated bonding) technique for connecting the die contact pads to the lead frame fingers. This technique is seen in U.S. Pat. Nos. 3,689,991 and 3,544,857 in which in the latter a tab of metallized polyimide is etched to form conducting pathways and the tab placed downward to bridge between die contact pads and the leads of a lead frame. The tab substitutes for the bonding wires. However, there are many other interconnect applications when it is desired to use bonding wires so as to not to incur the added expense and inconvenience of adding bonding bumps to the die and lead frame for proper bonding of the tab to the die and lead frames, respectively.